Geog Lecture 29 Mapping and GIS Continued

Transcription

1 Geog Lecture 29 Mapping and GIS Continued Today s Lecture (Pgs 13-25, 28-29) 1. Hand back Assignment 3 2. Review of Dr. Peddle s lecture last week 3. More on Geographic Information Systems 1

2 GIS Applications in Physical Geography For Example: A = Forest; B = Proposed urban development: Query: Show areas where urban development is proposed in a forested area Query: Show areas where forest will remain natural 2

3 GIS Applications in Physical Geography GIS Applications in Physical Geography And many others!! GIS Built on Coordinate Systems GIS Useful because it brings together spatial data: - many types, many sources Relationships between datasets: 1. Depends on spatial frame of reference as well as data. 2. Coordinate systems don t need to be the same Geographic: Projected: Coordinate Systems - Two Types: BUT Need to know how coordinate systems relate to each other. What is a coordinate system? A reference system that is used to represent the locations of objects on the Earth s surface and within a common geographic frame of reference. 3

4 Geographic Coordinate Systems: Projected Coordinate Systems: Location is determined from centre to a point on earth s surface. Measure in degrees indicates the angle. Decimal degrees or degrees, minutes, seconds Lines of Latitude: Horizontal lines running east to west Called parallels A flat, two dimensional surface where the distance between locations have constant lengths, angles, and areas. Mathematical transform used to project from 3D sphere to flat surface. Locations determined using x, y on a grid represent points on a horizontal and vertical axes: Lines of Longitude: Run north to south, have equal longitude. Called meridians Graticular network Latitude and Longitude grid. Projected Coordinate Systems: So when you see diagrams that look like this Or this Projected Coordinate Systems: From ArcGIS Resources. And some parts look really weird, stretched but others look well in perspective they are projected. (Don t bother memorizing all of the different types ) 4

5 Ellipsoid/Spheroid and the Geoid: Latitude and Longitude requires understanding of radius of Earth at locations: Not so easy Sir Isaac Newton first thought Earth was not spherical. Later confirmed with measurements Ellipsoid/Spheroid and the Geoid: The Geoid is a more accurate representation than the Spheroid(Ellipsoid). - Also includes elevation influences. Geoid Defined as the surface of the earth s gravity field Earth Model Gives us more accurate estimate of Earth geometry = more accurate latitude and longitude. Approx same as mean sea level. Varies perpendicular to pull of gravity. Mass of Earth varies gravity and shape of Earth also vary. - Geoid provides difference between Geoid and reference Ellipsoid. Difference is Geoid Height (N) e.g. N > 0 when geoid > ellipsoid; N < 0 when geoid < ellipsoid Allows conversion from ellipsoidal heights (h) to orthometric heights (H) (geoid - elevation). Datums: Based on the Spheroid If we vary the datum, coordinates change: E.g. Lethbridge: WGS84 / NAD deg long; deg lat. Same location in NAD deg long; deg lat. In UTM coordinates: easting; northing (Zone 12) NAD E; N (zone 12) NAD27 ** The same location using NAD83 is 5 m to the west of that location using NAD27 Map Scale, Resolution and Accuracy Two Different Types of Scale: Geographic Scale: Something that takes up a large area. E.g. Canada has a much larger geographic scale than Lethbridge Map Scale: The number of units on a map = the number of same units in the real world. Recall: 1:24,000 1 unit on the map = 24,000 of the same units on Earth. *A Representative Fraction. and is 219 m north of that same location using NAD27!! 5

6 Scale, Resolution and Accuracy A Large Scale Map: Shows a smaller geographic area. Scale fraction is larger e.g. 1:4000 scale map Scale, Resolution and Accuracy Scale allows for Generalisation: Reduces complexity, detail enhanced clarity 1:100,000 scale 1:24,000 scale A Small Scale Map: Shows a Larger geographic area. Scale fraction is smaller e.g. 1:250,000 scale map 20 times no. of lines 3 times total length of lines Scale how much information do you want to include? In A GIS Isn t formal Scale because you can zoom in and out! Craig Coburn River Basin Flow Lines 1:100,000 scale 557 lines, Total length 1890 km River Basin Flow Lines 1:24,000 scale 11,338 lines, Total length 5559 km What makes a good map??? Locating Objects on Earth and on Maps: Global Positioning Systems Description Title Legend Has 3 components: 1. Space segment: GPS satellites ( space vehicles ) orbiting Earth. 2 Orbits per day at 20,200 kms above earth. constellation Known position at precise time of signal transmission. Inset Scale Pleasing colours lines, balanced, etc. Spatial Reference system 6

7 Space Segment: Global Navigation Satellite System (GNSS) Satellites constellation: - Allows for enough visible satellites (24 satellite minimum) for full constellation. - Viewable by someone on earth location Position of interest triangulated from multi satellites, each emitting radio frequency signals from a known position Signals sent on carrier frequencies: L1 ( MHz) and L2 ( MHz) Clear view of sky important to allow line of site to satellites Has 3 components: Global Positioning Systems Control Segment Virtual base follows platform location 1. Space segment: GPS satellites ( space vehicles ) orbiting Earth. 2 Orbits per day at 20,200 kms above earth. consetallation Known position at precise time of signal transmission. 2. Control segment: Series of global ground control stations monitor and track satellite signals signals sent to central location for broadcasting OR CACS 7

8 Has 3 components: Global Positioning Systems User Segment 1. Space segment: GPS satellites ( space vehicles ) orbiting Earth. 2 Orbits per day at 20,200 kms above earth. consetallation Known position at precise time of signal transmission. 2. Control segment: Series of global ground control stations monitor and track satellite signals signals sent to central location for broadcasting 3. User segment: A GPS unit used by a person on Earth. Receives signals from satellites, but does not transmit. Information used to determine location. number of channels = number of satellite signals received. Can also read L1 and or L2 frequencies How Does GPS Find Your Position? Radio waves sent as Electromagnetic radiation : Measures transmission time from satellite (t) Knows that radio waves moving at speed of light (c) Reading for Friday: Pages Remote Sensing Therefore: t x c = distance (pseudorange) Trilateration Position determined based on three points of (satellite) reference: Get you a closer, more precise understanding of where you are. But in 3D (spherical distances) Intersection of 3 spheres improved using 4 th satellite 8